U.S. patent application number 15/095472 was filed with the patent office on 2017-05-04 for method of reducing noise of video signal.
This patent application is currently assigned to SAMSUNG SDS CO., LTD.. The applicant listed for this patent is SAMSUNG SDS CO., LTD.. Invention is credited to Jung-Ah CHOI, Jin-Ho CHOO, Seong-Jong HA, Sun-Ah KANG, Bo-Youn KIM, Yeon-Hee KWON, Young-Min SHIN, Jeong-Seon YI.
Application Number | 20170127088 15/095472 |
Document ID | / |
Family ID | 58635052 |
Filed Date | 2017-05-04 |
United States Patent
Application |
20170127088 |
Kind Code |
A1 |
CHOI; Jung-Ah ; et
al. |
May 4, 2017 |
METHOD OF REDUCING NOISE OF VIDEO SIGNAL
Abstract
Disclosed is a method for reducing noise. The method comprises
decoding a bitstream encoded with a first codec, acquiring
Quantization Parameter (QP) values determined in a process of
encoding the bitstream with the first codec, detecting a frame with
noise by using the QP values and inputting the frame with noise to
a predefined noise filter.
Inventors: |
CHOI; Jung-Ah; (Seoul,
KR) ; CHOO; Jin-Ho; (Seoul, KR) ; KIM;
Bo-Youn; (Seoul, KR) ; SHIN; Young-Min;
(Seoul, KR) ; HA; Seong-Jong; (Seoul, KR) ;
YI; Jeong-Seon; (Seoul, KR) ; KWON; Yeon-Hee;
(Seoul, KR) ; KANG; Sun-Ah; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SAMSUNG SDS CO., LTD. |
Seoul |
|
KR |
|
|
Assignee: |
SAMSUNG SDS CO., LTD.
Seoul
KR
|
Family ID: |
58635052 |
Appl. No.: |
15/095472 |
Filed: |
April 11, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04N 19/40 20141101;
H04N 19/86 20141101; H04N 19/117 20141101; H04N 19/172 20141101;
H04N 19/154 20141101 |
International
Class: |
H04N 19/86 20060101
H04N019/86; H04N 19/124 20060101 H04N019/124; G06K 9/62 20060101
G06K009/62; H04N 19/44 20060101 H04N019/44 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 29, 2015 |
KR |
10-2015-0151245 |
Claims
1. A method of reducing noise, comprising: decoding a bitstream
encoded with a first codec to obtain a decoded bitstream; acquiring
one or more Quantization Parameter (QP) values determined in a
process of encoding the bitstream with the first codec; detecting a
frame with noise by using the one or more QP values; and inputting
the frame with noise to a predefined noise filter.
2. The method of claim 1, wherein the detecting the frame with
noise, comprises determining a frame having a QP value that exceeds
a predefined threshold value, as the frame with noise.
3. The method of claim 1, wherein the acquiring the one or more QP
values, comprises acquiring the one or more QP values which are
respectively applied to frames that are sequentially displayed.
4. The method of claim 3, wherein the detecting the frame with
noise, comprises: calculating a first difference, which is a
difference between a first QP value of a first frame and a second
QP value of a second frame; calculating a second difference, which
is a difference between the second QP value of the second frame and
a third QP value of a third frame; and determining the second frame
as the frame with noise if each of the first and the second
differences exceed the predefined threshold value.
5. The method of claim 4, wherein the detecting the frame with
noise, further comprises: calculating a third difference, which is
a difference between the first QP value of the first frame and the
third QP value of the third frame; and determining the second frame
as the frame with noise if the first or the second difference
exceeds the third difference.
6. The method of claim 1, further comprising: encoding the decoded
bitstream with a second codec.
7. A noise reduction apparatus, comprising: a decoding unit
configured to decode a bitstream encoded with a first codec to
obtain a decoded bitstream; a QP acquisition unit configured to
acquire one or more QP values determined in a process of encoding
the bitstream with the first codec; a noise extraction unit
configured to detect a frame with noise by using the one or more QP
values; and a noise filtering unit configured to reduce noise from
the frame with noise; wherein the decoding unit, the QP acquisition
unit, the noise extraction unit and the noise filtering unit are
implemented by one or more processors.
8. The noise reduction apparatus of claim 7, wherein the noise
extraction unit is configured to determine a frame having a QP
value that exceeds a predefined threshold value as the frame with
noise.
9. The noise reduction apparatus of claim 7, wherein the QP
acquisition unit is configured to acquire the one or more QP values
which are respectively applied to frames that are sequentially
displayed.
10. The noise reduction apparatus of claim 9, wherein the noise
extraction unit is configured to calculate a first difference,
which is a difference between a first QP value of a first frame and
a second QP value of a second frame, and a second difference, which
is a difference between the second QP value of the second frame and
a third QP value of a third frame, and to determine the second
frame as the frame with noise if each of the first and the second
differences exceed the predefined threshold value.
11. The noise reduction apparatus of claim 10, wherein the noise
extraction unit is further configured to calculate a third
difference, which is a difference between the first QP value of the
first frame and the third QP value of the third frame, and
determines the second frame as the frame with noise if the first or
the second difference exceeds the third difference.
12. The noise reduction apparatus of claim 7, further comprising:
an encoding unit configured to encode the decoded bitstream with a
second codec.
13. A noise reduction apparatus, comprising: one or more
processors; a memory configured to store a computer program that is
executed by at least one of the one or more processors; and a
storage configured to store a noise reduction computer program
capable of reducing noise from a video signal, wherein the noise
reduction computer program comprises a set of instructions which
are executable by the one or more processor to: decode a bitstream
encoded with a first codec to obtain a decoded bitstream; acquire
one or more QP values determined in a process of encoding the
bitstream with the first codec; detect a frame with noise by using
the one or more QP values; and input the frame with noise to a
predefined noise filter.
14. A computer program stored in a non-transitory computer-readable
recording medium, for executing, in connection with a computing
device comprising at least a processor and a memory, the steps of:
decoding a bitstream encoded with a first codec to obtain a decoded
bitstream; acquiring one or more QP values determined in a process
of encoding the bitstream with the first codec; detecting a frame
with noise by using the one or more QP values; and inputting the
frame with noise to a predefined noise filter.
Description
[0001] This application claims priority to Korean Patent
Application No. 10-2015-0151245 filed on Oct. 29, 2015 in the
Korean Intellectual Property Office, the disclosure of which is
incorporated herein by reference in its entirety.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The invention relates to a method of reducing noise of a
video signal, and more particularly, to a method of reducing noise
of a video signal, which is capable of detecting and reducing noise
generated in a quantization step of an encoding process.
[0004] 2. Description of the Related Art
[0005] Noise reduction in a conventional video transcoding process
is performed by detecting noise using the intra-picture coding mode
or the motion vector of a block and filtering the noise.
[0006] However, the conventional noise reduction method cannot
detect noise resulting from variations in Quantization Parameters
(QPs) that may be encountered during an encoding process.
[0007] FIG. 1 is a schematic view for explaining noise that may be
generated in a conventional video transcoding system.
[0008] Referring to FIG. 1, the conventional video transcoding
system includes a camera 10 and a transcoder 20. The camera 10
includes an image pickup unit 11, which picks up an image, and a
first codec encoding unit 12, which converts a bitstream to an
arbitrary first codec to transmit the picked-up image.
[0009] The transcoder 20 receives the converted bitstream, decodes
the received bitstream using a first codec decoding unit 21, and
converts the decoded bitstream to a second codec using a second
codec encoding unit 22.
[0010] However, a transcoding process performed by the conventional
video transcoding system may include pickup noise 30, which is
generated during the pickup of an image by the image pickup unit
11, first quantization noise 40, which is generated during the
encoding of the image by the first codec encoding unit 12, and
second quantization noise 50, which is generated during the
encoding of the image by the second codec encoding unit 22.
[0011] Accordingly, the necessity of a method to reduce
quantization noise generated during the conversion of a bitstream
from an arbitrary first codec to an arbitrary second codec has
arisen.
SUMMARY
[0012] Exemplary embodiments of the invention provide a method of
reducing noise of a video signal, which is capable of reducing
noise generated in a quantization process.
[0013] Exemplary embodiments of the invention also provide a method
of reducing noise of a video signal, which is capable of improving
the similarities between frames and the compression rate of the
frames by extracting a frame with large noise so as to reduce
noise.
[0014] However, exemplary embodiments of the invention are not
restricted to those set forth herein. The above and other exemplary
embodiments of the invention will become more apparent to one of
ordinary skill in the art to which the invention pertains by
referencing the detailed description of the invention given
below.
[0015] According to an exemplary embodiment of the invention, there
is provided a method for reducing noise, the method comprising
decoding a bitstream encoded with a first codec, acquiring
Quantization Parameter (QP) values determined in a process of
encoding the bitstream with the first codec, detecting a frame with
noise by using the QP values and inputting the frame with noise to
a predefined noise filter.
[0016] In an embodiment of the present invention, wherein the
detecting the frame with noise, comprises determining a frame
having a QP value that exceeds a predefined threshold value as the
frame with noise.
[0017] In an embodiment of the present invention, wherein the
acquiring the QP values, comprises acquiring QP values respectively
applied to frames that are sequentially displayed.
[0018] In an embodiment of the present invention, wherein the
detecting the frame with noise, comprises: calculating a first
difference, which is the difference between a QP value of a first
frame and a QP value of a second frame, calculating a second
difference, which is the difference between the QP value of the
second frame and a QP value of a third frame and determining the
second frame as the frame with noise if the first and second
differences exceed the predefined threshold value.
[0019] In an embodiment of the present invention, wherein the
detecting the frame with noise, further comprises: calculating a
third difference, which is the difference between the QP value of
the first frame and the QP value of the third frame and determining
the second frame as the frame with noise if the first or second
difference exceeds the third difference.
[0020] In an embodiment of the present invention, the method
further comprising: encoding the bitstream with a second codec.
[0021] According to another aspect of the present invention, there
is provided a noise reduction apparatus comprising a decoding unit
decoding a bitstream encoded with a first codec, a QP acquisition
unit acquiring QP values determined in a process of encoding the
bitstream with the first codec, a noise extraction unit detecting a
frame with noise by using the QP values and a noise filtering unit
reducing noise from the frame with noise.
[0022] In an embodiment of the present invention, wherein the noise
extraction unit determines a frame having a QP value that exceeds a
predefined threshold value as the frame with noise.
[0023] In an embodiment of the present invention, wherein the QP
acquisition unit acquires QP values respectively applied to frames
that are sequentially displayed.
[0024] In an embodiment of the present invention, wherein the noise
extraction unit calculates a first difference, which is the
difference between a QP value of a first frame and a QP value of a
second frame, and a second difference, which is the difference
between the QP value of the second frame and a QP value of a third
frame, and determines the second frame as the frame with noise if
the first and second differences exceed the predefined threshold
value.
[0025] In an embodiment of the present invention, wherein the noise
extraction unit further calculates a third difference, which is the
difference between the QP value of the first frame and the QP value
of the third frame, and determines the second frame as the frame
with noise if the first or second difference exceeds the third
difference.
[0026] In an embodiment of the present invention, further
comprising: an encoding unit encoding the bitstream with a second
codec.
[0027] According to another aspect of the present invention, there
is provided a noise reduction apparatus comprising one or more
processors, a memory loading a computer program that is executed by
the processors and a storage storing a noise reduction computer
program capable of reducing noise from a video signal, wherein the
noise reduction computer program comprises: an operation decoding a
bitstream encoded with a first codec, an operation acquiring QP
values determined in a process of encoding the bitstream with the
first codec, an operation detecting a frame with noise by using the
QP values and an operation inputting the frame with noise to a
predefined noise filter.
[0028] According to another aspect of the present invention, there
is provided a computer program stored in a computer-readable
recording medium stored in a computer-readable recording medium,
for executing, in connection with a computing device, the steps of:
decoding a bitstream encoded with a first codec, acquiring QP
values determined in a process of encoding the bitstream with the
first codec, detecting a frame with noise by using the QP values
and inputting the frame with noise to a predefined noise
filter.
[0029] According to the exemplary embodiments, noise generated in a
quantization process can be reduced.
[0030] In addition, the similarities between frames and the
compression rate of the frames can be improved by extracting a
frame with large noise so as to reduce noise.
[0031] Other features and aspects will be apparent from the
following detailed description, the drawings, and the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a schematic view for explaining noise that may be
generated in a conventional video transcoding system.
[0033] FIG. 2 is a flowchart illustrating a method of reducing
noise according to an exemplary embodiment of the invention.
[0034] FIG. 3 is a block diagram for explaining a process of
acquiring the Quantization Parameter (QP) value of each frame
according to an exemplary embodiment of the invention.
[0035] FIG. 4 is a schematic view for explaining a method of
detecting a frame with noise according to an exemplary embodiment
of the invention.
[0036] FIG. 5 is a schematic view for explaining a method of
detecting a frame with noise according to another exemplary
embodiment of the invention.
[0037] FIG. 6 is a schematic view for explaining a method of
detecting a frame with noise according to another exemplary
embodiment of the invention.
[0038] FIGS. 7 and 8 are graphs for explaining a process of
increasing the compression rate of a video signal by detecting a
frame with noise and reducing noise.
[0039] FIG. 9 is a functional block diagram of a noise reduction
apparatus according to an exemplary embodiment of the
invention.
[0040] FIG. 10 is a functional block diagram of a noise reduction
apparatus according to another exemplary embodiment of the
invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0041] Advantages and features of the present invention and methods
of accomplishing the same may be understood more readily by
reference to the following detailed description of preferred
embodiments and the accompanying drawings. The present invention
may, however, be embodied in many different forms and should not be
construed as being limited to the embodiments set forth herein.
Rather, these embodiments are provided so that this disclosure will
be thorough and complete and will fully convey the concept of the
invention to those skilled in the art, and the present invention
will only be defined by the appended claims. Like numbers refer to
like elements throughout.
[0042] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
invention belongs. It will be further understood that terms, such
as those defined in commonly used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and the present
disclosure, and will not be interpreted in an idealized or overly
formal sense unless expressly so defined herein.
[0043] In addition, it will be understood that the singular forms
are intended to include the plural forms as well. It will be
further understood that the terms "comprises" and/or "comprising,"
when used in this specification, specify the presence of stated
features, integers, steps, operations, elements, and/or components,
but do not preclude the presence or addition of one or more other
features, operations, elements, and/or components thereof.
[0044] FIG. 2 is a flowchart illustrating a method of reducing
noise according to an exemplary embodiment of the invention.
[0045] The exemplary embodiment of FIG. 2 will hereinafter be
described, taking a bitstream encoded with an arbitrary first codec
as an example. The first codec may be implemented in various types
capable of compressing a video signal.
[0046] In response to a bitstream encoded with the first codec
being received, the bitstream is decoded (S210). The decoding of
the bitstream may be performed by performing steps of the encoding
of the bitstream in reverse order. More specifically, video
information of a spatial domain may be generated by {circle around
(1)} converting compressed encoded values into symbols, {circle
around (2)} performing inverse quantization so as to acquire
Discrete Cosine Transform (DCT) coefficients, and {circle around
(3)} performing inverse DCT.
[0047] A noise reduction apparatus according to an exemplary
embodiment of the invention acquires Quantization Parameter (QP)
values (S220) determined in the process of encoding the bitstream
with the first codec.
[0048] A QP is needed to inversely quantize symbol-type encoded
values and thus to acquire DCT coefficients. Accordingly, QP
information regarding QP values set in the process of compressing a
video signal with the first codec is included in the bitstream
encoded with the first codec.
[0049] An encoder may acquire DCT coefficients by performing DCT on
an N.times.N pixel block of an arbitrary frame. A process of
dividing the DCT coefficients by a predetermined value to remove
high-frequency components that are of less importance is referred
to as quantization, and the predetermined value is referred to as
the QP.
[0050] Accordingly, the noise reduction apparatus may acquire QP
values from the bitstream encoded with the first codec. More
specifically, the aforementioned encoding process is performed in
units of frames of a video signal, and the noise reduction
apparatus may acquire the QP value of each of the frames.
[0051] Different frames may have different QP values. For example,
a relatively large QP value may be applied to a frame whose
compression rate needs to be increased according to the size of
bandwidth for transmitting a bitstream, and a relatively small QP
value may be applied to a frame whose compression rate does not
need to be increased.
[0052] Accordingly, a first frame may be quantized with a first QP
value, and a second frame, which is different from the first frame,
may be quantized with a second QP value, which is different from
the first QP value.
[0053] Once the QP value of each frame is acquired, a frame with
noise is extracted using the QP value of each frame. More
specifically, a frame having a QP value larger than a predefined
threshold value may be extracted as a frame with noise (S230).
[0054] In the case of a frame with a relatively large QP value, a
large amount of data is likely to be lost from the frame in the
process of increasing the compression rate of the frame, and thus,
a large amount of noise may be generated in the frame after the
decoding of the frame due to the data loss.
[0055] Thus, a frame with a QP value that exceeds the predefined
threshold value may be extracted as a frame with noise.
[0056] Once the frame with noise is extracted, noise is reduced by
inputting the extracted frame to a noise filter (S240). The noise
filter may be a Low Pass Filter (LPF), but the invention is not
limited thereto. That is, various other general-purpose filters
capable of reducing noise may also be used.
[0057] In short, the bitstream encoded with the first codec may be
decoded, noise caused by the QP may be reduced during the decoding
of the bitstream encoded with the first codec, and the decoded
bitstream is encoded back with a second codec, thereby performing
transcoding.
[0058] According to the exemplary embodiment of FIG. 2, noise
caused by the QP may be reduced, and the compression rate of a
video signal may be improved when performing transcoding with the
second codec.
[0059] A process of increasing the compression rate of a video
signal by reducing noise will be described later with reference to
FIGS. 7 and 8.
[0060] FIG. 3 is a block diagram for explaining a process of
acquiring the QP value of each frame according to an exemplary
embodiment of the invention.
[0061] Referring to FIG. 3, compressed data 310 may be a video
signal encoded with a first codec, i.e., a bitstream. The
compressed data 310 may be a code consisting of 0s and 1s and may
include brightness and color components of the video signal.
[0062] An entropy decoder 320 receives the compressed data 310 and
converts the compressed data into original symbol values. The
symbol values are values acquired by quantizing DCT coefficients
during an encoding process.
[0063] An inverse quantizer 330 inversely quantizes the symbol
values and thus outputs DCT coefficients. In order for the inverse
quantizer 330 to perform inverse quantization, QP values used in a
quantization process are needed.
[0064] The compressed data 310 includes QP information regarding a
QP value applied to each frame of the video signal. Accordingly,
the noise reduction apparatus may acquire the QP value of each
frame from the compressed data 310, i.e., the bitstream.
[0065] Thereafter, the inverse quantizer 330 outputs DCT
coefficients yet to be quantized, and an inverse discrete cosine
transformer 340 outputs a video signal 350 including video
information of a spatial domain.
[0066] FIG. 4 is a schematic view for explaining a method of
detecting a frame with noise according to an exemplary embodiment
of the invention.
[0067] Referring to FIG. 4, a first frame 410, a second frame 420,
and a third frame 430 may be consecutive frames that are
sequentially displayed. That is, since a video signal is a set of
pictures that are consecutively captured within a given period of
time, the first, second, and third frames 410, 420, and 430 may be
perceived as a motion video when displayed one after another.
[0068] The noise reduction apparatus may acquire a QP value applied
to each frame by performing the decoding process described above
with reference to FIG. 3.
[0069] If the QP value of a particular frame exceeds a predefined
threshold value, the particular frame may be determined as a frame
with noise. As mentioned above, the larger the QP value of the
particular frame, the larger the amount of high-frequency
components removed from the particular frame. That is, the larger
the QP value of the particular frame, the larger the amount of data
lost during a compression process. Accordingly, if the particular
frame is decoded, a large amount of noise may be included in the
particular frame. Therefore, a frame having a QP value that exceeds
the predefined threshold value may be determined as a frame with
noise.
[0070] For example, if a QP value QP.sub.cur of the second frame
420 exceeds the predefined threshold value, the second frame 420
may be determined as a frame with noise.
[0071] However, the invention is not limited to the exemplary
embodiment of FIG. 4, but may be implemented in various other
manners.
[0072] FIG. 5 is a schematic view for explaining a method of
detecting a frame with noise according to another exemplary
embodiment of the invention.
[0073] Referring to FIG. 5, a first frame 410, a second frame 420,
and a third frame 430 may be sequentially displayed, as already
mentioned in the exemplary embodiment of FIG. 4. That is, a motion
video may be played by displaying the first frame 410, then
displaying the second frame 420, and then displaying the third
frame 430.
[0074] The noise reduction apparatus calculate a first difference,
which is the difference between the QP value of the first frame 410
and the QP value of the second frame 420, and a second difference,
which is the difference between the QP value of the second frame
420 and the QP value of the third frame 430.
[0075] More specifically, the first and second differences may be
calculated by Equations (1) and (2), respectively, as illustrated
in FIG. 5:
dQP.sub.cur-prev=|QP.sub.cur-QP.sub.prev| (1); and
dQP.sub.cur-next=|QP.sub.cur-QP.sub.next| (2).
where dQP.sub.cur-prev denotes the first difference, QP.sub.cur
denotes the QP value of the second frame 420, QP.sub.prev denotes
the QP value of the first frame 410, dQP.sub.cur-next denotes the
second difference, and QP.sub.next denotes the QP value of the
third frame 430.
[0076] Thereafter, if the first and second differences exceed a
predefined threshold value, the second frame 420 may be determined
as a frame with noise.
[0077] That is, in a case where the first and second differences
both exceed the predefined threshold value, the QP value of the
second frame 420 is much larger than the QP value of the first
frame 410 and the QP value of the third frame 430.
[0078] In this case, a bitstream corresponding to the second frame
420 may be in a state of having a large amount of high-frequency
components removed therefrom. Thus, if the bitstream is decoded, a
large amount of noise may be included in the second frame 420.
[0079] According to the exemplary embodiment of FIG. 5, a frame
with a large amount of noise may be detected.
[0080] FIG. 6 is a schematic view for explaining a method of
detecting a frame with noise according to another exemplary
embodiment of the invention.
[0081] Referring to FIG. 6, the noise reduction apparatus may
calculate not only first and second differences, but also a third
difference, which is the difference between the QP value of a first
frame 410 and the QP value of a third frame 430.
[0082] The QP value of the third frame 430 may be calculated by
Equation (3), as illustrated in FIG. 6:
dQP.sub.prev-next=|QP.sub.prev-QP.sub.next| (3)
where dQP.sub.prev-next denotes the third difference, QP.sub.prev
denotes the QP value of the first frame 410, and QP.sub.next
denotes the QP value of the third frame 430.
[0083] In a case where the QP value of a second frame 420 is much
larger than the QP value of the first frame 410 and the QP value of
the third frame 430, the first or second difference may exceed the
third difference.
[0084] As already mentioned above, since a frame with a large QP
value includes a large amount of noise, the second frame 420 may be
determined as a frame with noise.
[0085] Once a frame with noise is detected using at least one of
the methods of FIGS. 4 through 6, the frame may be input to a
filter so as to reduce noise.
[0086] A method of reducing noise by inputting a frame with noise
to a filter is already well known and obvious to a person skilled
in the art to which the invention pertains, and thus, a detailed
description thereof will be omitted.
[0087] In short, by detecting a frame with noise and reducing
noise, the similarities between consecutive frames of a video
signal may be enhanced. As a result, the compression rate of the
video signal may be improved when transcoding a decoded bitstream
with a second codec.
[0088] FIGS. 7 and 8 are graphs for explaining a process of
increasing the compression rate of a video signal by detecting a
frame with noise and reducing noise.
[0089] There is a method of compressing a video signal using
inter-frame temporal correlations. This method reduces the size of
a video based on the fact that adjacent frames are generally very
similar.
[0090] A 24 Frames Per Second (FPS) video signal includes 24 frames
for a one-second period. That is, since a motion video is played by
exposing similar frames for a short period of time, pixels from
temporally adjacent frames are highly likely to have similar
values.
[0091] That is, the more similar the temporally adjacent frames of
a video signal are to each other, the higher the compression rate
of the video signal becomes. On the other hand, if too much noise
is included in an arbitrary frame, the similarities between the
arbitrary frame and its previous and subsequent frames may be
lowered, and as a result, the compression rate of the video signal
may also be lowered.
[0092] Referring to FIG. 7, the X axis represents frames that are
sequentially displayed, and the Y-axis represents the size in bits
of the frames.
[0093] A fifth frame 720 has a large size in bits than the other
frames, and this may be due to an excessive quantization of a
fourth frame 710 that is temporally adjacent to the fifth frame
720.
[0094] That is, if the fourth frame 710 is quantized by applying a
large QP value to the fourth frame 710, a large amount of
high-frequency components may be removed from the fourth frame 710,
and as a result, a large amount of data may be lost from the fourth
frame 710. Then, if the fourth frame 710 is decoded, an excessive
number of noise may be generated, and due to this noise, the
similarity between the fourth frame 710 and the fifth frame 720 may
be lowered.
[0095] Accordingly, the compression rate of the fifth frame 720 may
decrease, and thus, the fifth frame 720 may have a larger size in
bits than the other frames. If the noise of the fourth frame 710 is
reduced by the method according to the exemplary embodiment of FIG.
2, the similarity between the fourth frame 710 and the fifth frame
720 may be improved, and thus, the size in bits of the fifth frame
720 may be reduced.
[0096] More specifically, referring to FIG. 8, in response to the
noise of the fourth frame 710 being reduced, the similarity between
the fourth frame 710 and the fifth frame 720 may be improved, and
thus, the bitrate of the fifth frame 720 may be lowered.
[0097] FIG. 9 is a functional block diagram of a noise reduction
apparatus according to an exemplary embodiment of the
invention.
[0098] Referring to FIG. 9, a noise reduction apparatus 900
includes a decoding unit 910, a QP acquisition unit 920, a noise
extraction unit 930, and a noise filtering unit 940. FIG. 9
illustrates only the elements of the noise reduction apparatus 900
that are relevant to the invention. Accordingly, it is obvious that
the noise reduction apparatus 900 may also include other
general-purpose elements than those illustrated in FIG. 9.
[0099] The decoding unit 910 decodes a bitstream encoded with a
first codec. More specifically, the decoding unit 910 generates
video information of a spatial domain by {circle around (1)}
converting compressed encoded values into symbols, {circle around
(2)} performing inverse quantization so as to acquire DCT
coefficients, and {circle around (3)} performing inverse DCT.
[0100] The QP acquisition unit 920 acquires QP values that have
been determined in the process of encoding the bitstream with the
first codec. The QP values are included in the bitstream encoded
with the first codec. The QP values may be set to differ from one
frame to another frame.
[0101] The noise extraction unit 930 extracts a frame with noise
using the QP values. The noise extraction unit 930 may determine a
frame having a QP value that exceeds a predefined threshold value
as the frame with noise. Alternatively, the noise extraction unit
930 may detect the frame with noise by calculating the differences
between the QP values of consecutive frames.
[0102] A method of detecting the frame with noise by calculating
the differences between the QP values of consecutive frames has
already been described above with reference to FIGS. 4 through 6,
and thus, a detailed description thereof will be omitted.
[0103] Once the noise extraction unit 930 detects the frame with
noise, the noise filtering unit 940 inputs the frame with noise to
a filter so as to filter the noise.
[0104] The noise filtering unit 940 may be provided as an LPF, but
the invention is not limited thereto. That is, the noise filtering
unit 940 may also be provided as a general-purpose filter, other
than an LPF, capable of reducing noise.
[0105] The noise reduction apparatus 900 may also include an
encoding unit (not illustrated), which decodes the bitstream
encoded with the first codec for transcoding and then encodes the
resulting video signal with noise reduced therefrom back with a
second codec.
[0106] The noise reduction apparatus 900 may reduce noise that may
be generated in a quantization process. Also, by reducing the
noise, the noise reduction apparatus 900 may enhance the
similarities between frames and may thus improve the compression
rate of the frames.
[0107] FIG. 10 is a functional block diagram of a noise reduction
apparatus according to another exemplary embodiment of the
invention.
[0108] Referring to FIG. 10, a noise reduction apparatus 1000
includes a processor 1010, a storage 1020, a memory 1030, a network
interface 1040, and a bus 1050. FIG. 10 illustrates only the
elements of the noise reduction apparatus 1000 that are relevant to
the invention. Accordingly, it is obvious that the noise reduction
apparatus 1000 may also include other general-purpose elements than
those illustrated in FIG. 10.
[0109] The processor 1010 executes a noise reduction program
capable of reducing noise from a video signal. However, a program
that can be executed by the processor 1010 is not particularly
limited. That is, various other general-purpose programs may also
be executed by the processor 1010.
[0110] The storage 1020 stores the noise reduction program. The
storage 1020 may also store in advance information regarding a
predefined threshold value for detecting a frame with noise. More
specifically, a frame with noise may be detected by comparing the
QP value of the frame with the predefined threshold value, and
thus, the predefined threshold value may be stored in advance in
the storage 1020.
[0111] The noise reduction program executes the steps of: decoding
a bitstream encoded with a first codec; acquiring QP values
determined in the process of encoding the bitstream with the first
codec; detecting a frame with noise by using the QP values; and
inputting the frame with noise to a predefined noise filter.
[0112] The memory 1030 loads the noise reduction program and thus
allows the noise reduction program to be executed in the processor
1010.
[0113] Various computing devices may be connected to the network
interface 1040, and the bus 1050 serves as a data transfer path to
which the processor 1010, the storage 1020, the memory 1030, and
the network interface 1040 are all connected.
[0114] The method of reducing noise according to the present
invention can be recorded in programs that can be executed on a
computer and be implemented through general purpose digital
computers. In addition, the data format used in the method for
generating the web page according to the present invention may be
recorded in a computer-readable recording medium using various
means. Examples of the computer-readable recording medium may
include recording media such as magnetic storage media (e.g., ROMs,
floppy disks, hard disks, etc.) and optical recording media (e.g.,
CD-ROMs or DVDs).
[0115] While the present invention has been particularly shown and
described with reference to exemplary embodiments thereof, it will
be understood by those of ordinary skill in the art that various
changes in form and details may be made therein without departing
from the spirit and scope of the present invention as defined by
the following claims. It is therefore desired that the present
embodiments be considered in all respects as illustrative and not
restrictive, reference being made to the appended claims
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